Abrasive Media: Types and Choice

September 4, 2018

Abrasive Media: Types and Choice

Which Abrasive Media is Right for Your Project?

When finishing a project with a blasting, barrel tumbler, or vibratory system, you’ll need to identify the abrasive media required to achieve your desired surface finish. Abrasive media is the material used in conjunction with finishing equipment to clean, smooth, or polish the surface of a part. There are many different types of abrasive media that can be used for finishing, and each type will yield different surface results. The type of abrasive media you select can also impact the quality of any coating applied after, both in the near-term and down the road. It goes without saying: it’s important to choose wisely!

Choosing Your Abrasive Media

Abrasive medias can range in composition and size. In fact, you might be surprised at the things that can be used to finish a surface.

Start by identifying the surface finish you wish to achieve. Is there a certain level of roughness or shine that your project requires, or that you prefer?

If you’re not sure about the exact surface style, test out a softer abrasive media first. This will help ensure that the surface isn’t subject to any unwanted scratches or over-etching from a hard media you haven’t used before. Corn cob grit and walnut shell grit can be affordable, environmentally-friendly soft medias that are ideal for testing. Consider using these materials especially when finishing wood surfaces and softer metals. Crushed glass grit is another good option for wood projects, as are glass beads. In fact, glass is an abrasive media that can be used up to 100 times before it needs to be replaced. Talk about longevity!

After glass, the next hardest abrasive medias include pumice, garnet, and aluminum oxide grit (among others). As you consider these harder medias (a chart of medias and their hardness can be found here), you’ll want to think about how they’ll affect your surface’s “depth profile.”

Depth profile refers to a surface’s indentation pattern. Depth or surface profile is relevant because sometimes surfaces require certain depth profiles for a coating to stick properly. To achieve the right depth profile, abrasive medias are used to create specific indentation patterns that work best for the coating. If you’re dealing with a surface that’s hard and flat, like those made of steel, depth profile can be particularly important. For a coating to be properly applied, the coating should be able to fill the valleys completely and cover the peaks of the indentations. Note that a required depth profile should be identified at the outset of your project.

Generally speaking, the harder the abrasive media, the more significant the depth profile created. The hardest types of abrasive media include silicone carbide grit and aluminum oxide grit. As you evaluate hardness, also consider density. Dense media will absorb less energy upon impact with your project’s surface; instead, expending that energy on the surface and creating more significant etching.

Another factor to consider when selecting abrasive media? Size. The larger your abrasive media particles, the deeper the depth profiles they create. To that same point, the smaller your abrasive media particles, the shallower the depth profile. Keep this in mind when you look at medias with similar hardness, but different sizes.

You can also narrow down your abrasive media options by the edging of their particles. Angular particles will result in faster cleaning and the ability to cut through rust. Rounded particles will create more even surfaces that can break apart brittle coatings on top surface layer.

So, let’s regroup on the general rule of thumb when it comes to abrasive media: the larger, the denser, the more angular, and the harder a media, the more impact it will have on your project’s surface. If your project requires a surface with high depth profile, look for abrasive medias with these attributes. If a lighter etching is warranted, seek out their opposites! Keep in mind, however, that abrasive medias may have attributes that vary widely, which is why it never hurts to seek out guidance from finishing professionals.